This invention relates to improvements in a valve timing control system for hydraulically operating the opening and closing timings of intake and exhaust valves of an internal combustion engine, and more particularly to the valve timing control system of the type wherein a driving force is transmitted from a first camshaft to a second camshaft in the engine.
In recent years, a valve timing control system for an internal combustion engine of the type having two camshafts (first and second camshafts) on a cylinder head has been developed and disclosed in Japanese Patent Provisional Publication No. 9-280020. In this valve control system, the two camshafts are connected through a rotation control mechanism in a manner to be operated in timed relation to each other.
The valve timing control system disclosed in the Publication No. 9-280020 is arranged as follows: A vane rotor of the rotation control mechanism is installed together with a first driving force transmission member (sprocket or the like) to an end section of the first camshaft. A second driving force transmission member (gear or the like) is integrally fixed to a housing of the rotation control mechanism. The first driving force transmission member is driveably connected to a crankshaft, while the second driving force transmission member is drivingly connected to the second camshaft. Accordingly, the driving force input from the crankshaft to the first driving force transmission member is directly input to the first camshaft and further transmitted to the second camshaft through the rotation control mechanism and the second driving force transmission member.
In case of this valve timing control system, the vane rotor and the first driving force transmission member are formed with a central through-hole, and fitted on the first camshaft in such a manner that the first camshaft pierces the central through-hole, in which they are thrust against an engagement flange formed on the first camshaft. In other words, the engagement flange has been previously formed on the first camshaft at a position close to the end section of the first camshaft. A cam bolt is screwed into the first camshaft under a condition where the vane rotor and the first driving force transmission member are fitted on the end section of the first camshaft, so that the vane rotor and the first driving force transmission member are fastened and fixed between the head section of the cam bolt and the engagement flange.
However, drawbacks have been encountered in the conventional valve timing control system disclosed in the Publication No. 9-280020, in which the first camshaft must be integrally formed with the engagement flange against which the vane rotor and the first driving force transmission member are thrust to be fastened and fixed in position. This increases a production cost for the first camshaft.
It is an object of the present invention to provide an improved valve timing control system for an internal combustion engine, which can overcome drawbacks encountered in conventional valve timing control systems.
Another object of the present invention is to provide an improved valve timing control system for an internal combustion engine, in which a vane rotor of a rotation control mechanism and a driving force transmission member can be securely installed to a camshaft without inviting a rise in production cost and deformation of a cam bolt for fixing the vane rotor and the driving force transmission member to the camshaft.
A further object of the present invention is to provide an improved valve timing control system for an internal combustion engine, in which load applied to a vane rotor of a rotation control mechanism and a driving force transmission member is supported on the end section of a camshaft thereby preventing the load from being applied to a cam bolt.
An aspect of the present invention resides in a valve timing control system for an internal combustion engine. The valve timing control system comprises a rotation control mechanism comprising a housing, and a vane rotor which is rotatably disposed inside the housing and has at least one vane section. The vane section defines a first chamber and a second chamber which are located on opposite sides of the vane section, a hydraulic pressure being selectively supplied to and released from the first chamber and the second chamber so as to controllably accomplish a relative rotation of the vane rotor to the housing. The vane rotor is formed at its axially end section with a depression. A first camshaft is connected to the vane rotor by a cam bolt piercing the vane rotor along an axis of the vane rotor. A second camshaft is disposed parallel with the first camshaft. A first driving force transmission member is installed to the housing and connected to one of a crankshaft and the second camshaft. The housing of the rotation control mechanism has the first driving force transmission member. Additionally, a second driving force transmission member is installed to an end section of the first camshaft together with the vane rotor by the cam bolt and connected to the other of the crankshaft and the second camshaft. The second driving force transmission member comprises a generally cup-shaped section which has a cylindrical wall portion fitted on the end section of the first camshaft and fitted in the depression of the vane rotor. In the above arrangement, the vane rotor of the rotation control mechanism and the generally cup-shaped section of the second driving force transmission member are fixed together to the end section of the first camshaft upon tightening the cam bolt.
Another aspect of the present invention resides in a valve timing control system for an internal combustion engine. The valve timing control system comprises a rotation control mechanism comprising a casing, and a vane rotor which is rotatably disposed inside the housing. The vane rotor comprises a generally cylindrical body section, and at least one vane section integral with and radially extending from the cylindrical body section. The vane section defines a timing-advancing chamber and a timing-retarding chamber which are located on opposite sides of the vane section, the vane rotor making a relative rotation to the housing in a first direction for advancing a valve timing upon supply of hydraulic pressure into the timing-advancing chamber, the vane rotor making a relative rotation to the housing in a second direction for retarding the valve timing upon supply of hydraulic pressure into the timing-retarding chamber, the second direction being opposite to the first direction. The vane rotor is formed at its axially end section with a depression generally coaxial with the cylindrical body section. A change-over valve is provided and arranged such that a hydraulic pressure is selectively supplied through the change-over valve to the timing-advancing chamber and the timing-retarding chamber in accordance with an engine operating condition. A first camshaft is coaxially connected to the body section of the vane rotor by a cam bolt piercing the body section of the vane rotor along an axis of the vane rotor. A second camshaft is disposed parallel with the first camshaft. A first driving force transmission member is coaxially installed to the housing and connected to one of a crankshaft and the second camshaft. The housing of the rotation control mechanism has the first driving force transmission member. Additionally, a second driving force transmission member is coaxially installed to an end section of the first camshaft together with the vane rotor by the cam bolt and connected to the other of the crankshaft and the second camshaft. The second driving force transmission member comprises a generally cup-shaped section which comprises a cylindrical wall portion coaxial with the cylindrical body section of the vane rotor. The cylindrical wall portion is coaxially fitted on the end section of the first camshaft and has an end part fitted in the depression of the vane rotor of the rotation control mechanism. In the above arrangement, the vane rotor of the rotation control mechanism and the generally cup-shaped section of the second driving force transmission member are fixed together to the end section of the first camshaft upon tightening the cam bolt.
In the above valve timing control system according to the present invention, the second driving force transmission member is fitted and supported at its cup-shaped section on the end section of the camshaft. Additionally, the vane rotor is fitted and supported through the cup-shaped section of the second driving force transmission member on the end section of the camshaft. Accordingly, load applied to the vane rotor and the second driving force transmission member is supported on a fitting section at the end section of the camshaft though the vane rotor and the second driving force transmission member are fixed to the end section of the cam bolt under fastening of the cam bolt.
A further aspect of the present invention resides in a V-type internal combustion engine having first and second banks of cylinders. The engine comprises a first exhaust valve-side camshaft for driving exhaust valves, disposed in the first bank. A second exhaust valve-side camshaft is provided for driving exhaust valves, disposed in the second bank. A first intake valve-side camshaft is provided for driving intake valves, and is disposed in the first bank and located inside relative to the first exhaust valve-side camshaft, the first intake valve-side camshaft being parallel with the first exhaust valve-side camshaft. A second intake valve-side camshaft is provided for driving intake valves and disposed in the second bank and located inside relative to the second exhaust-side camshaft, the second intake valve-side camshaft being parallel with the second exhaust valve-side camshaft. A first rotation control mechanism is provided comprising a housing, and a vane rotor which is rotatably disposed inside the housing and has at least one vane section. The vane section defines a first chamber and a second chamber which are located on opposite sides of the vane section, hydraulic pressure being selectively supplied to and released from the first chamber and the second chamber so as to controllably accomplish a relative rotation of the vane rotor to the housing. The vane rotor is formed at its axially end section with a depression. The vane rotor is connected to the first exhaust valve-side camshaft by a cam bolt piercing the vane rotor along an axis of the vane rotor. A first driving force transmission member is connected to one of a crankshaft and the first intake valve-side camshaft. The housing of the first rotation control mechanism has the first driving force transmission member. A second driving force transmission member is installed to an end section of the first exhaust valve-side camshaft together with the vane rotor by the cam bolt and connected to the other of the crankshaft and the first intake valve-side camshaft. The second driving force transmission member comprises a generally cup-shaped section which has a cylindrical wall portion fitted on the end section of the first exhaust valve-side camshaft and fitted in the depression of the vane rotor, wherein the vane rotor of the first rotation control mechanism and the generally cup-shaped section of the second driving force transmission member are fixed together to the end section of the first exhaust valve-side camshaft upon tightening the cam bolt.
Additionally, the V-type internal combustion engine comprises a second rotation control mechanism which comprises a housing, and a vane rotor which is rotatably disposed inside the housing and has at least one vane section. The vane section defines a first chamber and a second chamber which are located on opposite sides of the vane section, hydraulic pressure being selectively supplied to and released from the first chamber and the second chamber so as to controllably accomplish a relative rotation of the vane rotor to the housing. The vane rotor is formed at its axially end section with a depression. The vane rotor is connected to the second exhaust valve-side camshaft by a cam bolt piercing the vane rotor along an axis of the vane rotor. A third driving force transmission member is connected to one of the crankshaft and the second intake valve-side camshaft. The housing of the second rotation control mechanism has the third driving force transmission member. Additionally, a fourth driving force transmission member is installed to an end section of the second exhaust valve-side camshaft together with the vane rotor by the cam bolt and connected to the other of the crankshaft and the second intake valve-side camshaft. The fourth driving force transmission member comprises a generally cup-shaped section which has a cylindrical wall portion fitted on the end section of the second exhaust valve-side camshaft and fitted in the depression of the vane rotor, wherein the vane rotor of the second rotation control mechanism and the generally cup-shaped section of the fourth driving force transmission member are fixed together to the end section of the second exhaust valve-side camshaft upon tightening the cam bolt.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.